A blind bandwidth extension technology is a technology at a decoder, and a decoder performs blind bandwidth extension according to a low-frequency decoding signal and by using a corresponding prediction method.
During ACELP encoding and decoding of a medium and low rate wideband, existing algorithms all first down-sample a wideband signal sampled at 16 kHz to 12.8 kHz, and then perform encoding. In this way, bandwidth of a signal output after the encoding and decoding is only 6.4 kHz. If an original algorithm is not changed, information in a part with a bandwidth of 6.4 to 8 kHz or 6.4 to 7 kHz needs to be recovered in a manner of the blind bandwidth extension, that is, corresponding recovery is performed only at the decoder.
However, a high frequency band signal recovered by the existing blind bandwidth extension technology deviates much from an original high frequency band signal, causing that the recovered high frequency band signal is unsatisfactory.